The infection is caused by a virus. The virus is spread to humans from the bite of an infected mosquito. Rarely it has spread from an infected blood transfusion, organ transplant, and breastfeeding.

Risk Factors

Things that raise the risk of WNV are:

Spending time outdoors—in areas with mosquitoes
Not using insect repellent
Mosquitoes in the home
Certain gene defects—that may make some people get infected more easily

Severe WNV is more common in men and people over 50 years old. Other things that raise the risk of severe WNV are:

A weak immune system
High blood pressure
Diabetes
Cancer
Kidney disease
Alcohol abuse disorder

Mosquito Bite

Symptoms

Most people with WNV have no symptoms. Others develop flu-like symptoms such as:

Fever and chills
Headache
Muscle pain
Nausea and vomiting
Diarrhea
Rash
Swollen lymph nodes
Eye inflammation— conjunctivitis

Symptoms can last from a few days to several weeks.

A small number of people with WNV develop serious symptoms, such as:

Headache and sensitivity to light
High fever
Stiff neck
Confusion
Lack of responsiveness or coma
Uncontrolled body movements
Muscle weakness, or not being able to move

Diagnosis

The doctor will ask about your symptoms, travel, and health history. A physical exam will be done.

WNV is often diagnosed with:

Blood tests
Lumbar puncture— some fluid around the brain and spinal cord is taken and tested

Other tests may be done, depending on symptoms.

Treatment

There is no specific treatment for WNV. Treatment depends on how severe the disease is. The goal is to manage symptoms and problems. In severe cases, hospital care is needed.

Depending on the symptoms, options may be:

Pain medicines
Medicine to ease nausea and vomiting
Fluids by mouth or IV—to treat dehydration

Treatment for severe symptoms may include:

Mechanical ventilation
Medicine to control seizures
Medicine to decrease brain swelling

Prevention

WMV can be prevented by avoiding mosquito bites. Things that may help are:

Covering up the skin
Using bug sprays, netting, and screens
Staying inside between dusk and dark

RESOURCES:

Centers for Disease Control and Prevention
https://www.cdc.gov

Infectious Diseases Society of America
http://www.idsociety.org

CANADIAN RESOURCES:

Alberta Ministry of Health
https://www.alberta.ca/health.aspx

Health Canada
https://www.canada.ca

References:

Mosquito avoidance. EBSCO DynaMed website. Available at: https://www.dynamed.com/prevention/mosquito-avoidance. Accessed April 5, 2021.

Sejvar JJ. West nile virus infection. Microbiol Spectr. 2016;4(3).

West Nile virus infection. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/west-nile-virus-infection . Accessed April 5, 2021.

West Nile virus: What you need to know. Centers for Disease Control and Prevention website. Available at: https://www.cdc.gov/westnile/index.html. Accessed April 5, 2021.

Last reviewed December 2020 by EBSCO Medical Review Board David L. Horn, MD, FACP
Last Updated: 4/5/2021

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